Disc brake calipers are arranged astride of a brake disc and are fixed on the inner side of a vehicle so as to be projecting on the outer side of the vehicle facing the associable wheel. On both sides of the caliper body there are arranged pads that act on braking surfaces of the brake disc, perpendicular to the axis of rotation of the brake disc. The axis of rotation of the brake disc and of the wheel defines an axial direction. Pads are pushed by pistons, seated in special seats, in abutment against the braking surfaces. The caliper body exhibits a seating window for the pads and for the disc portion influenced by the pads, the window allowing aeration for disposing of the heat generated by the braking.
Disc brake calipers in high performance vehicles are subject to considerable stress, both thermal and mechanical. The deformations of the caliper body in the braking step essentially are due to axial forces exchanged with the pushing pistons of the pads and to tangential forces exchanged between the pads and the braking band of the brake disc. The axial forces tend to open the caliper body making it take a “barrel” configuration, while the tangential forces tend to deform the caliper body as a “parallelogram,” a phenomenon known as “twisting” of the caliper body. The axial opening of the caliper body tends to decrease the braking sensitivity, the actuating stroke of the brake control being equal. The is twisting essentially due to the forces transmitted by the pads of the external half caliper due to the arm provided between the reaction point of the braking torque and the caliper body supports. The deformations of the caliper body, and in particular those of “twisting,” negatively affect the roll-back, that is, the moving back of the pad pushing pistons at the end of the braking step, causing sticking of the pads and relevant abnormal wear.
In order to oppose the deformations of the caliper body, it is possible to use a central bridge that extends astride of the brake disc and perpendicular thereto so as to connect the two half calipers to each other, respectively on the connection side and on the wheel side. Central bridges having large thicknesses, especially in tangential direction, are used in calipers for high performance vehicles. Solutions of central bridges that completely cover the window of seating space of the pads, provided with openings for heat venting, also are known. Such solutions imply the use of very cumbersome and heavy central bridges that excessively increase the mass of the caliper body and limit heat disposal.
The large mass of the caliper body and the poor heat disposal considerably disadvantage the high performance vehicles that require particularly small non-suspended masses, for improving the dynamic behavior of the vehicle, and a high heat disposal capacity of the caliper body to prevent hazardous “fading” phenomena. The “fading” essentially consists in a decrease of the braking effect, the brake control stroke being equal, and in extreme cases it can even lead to the inefficiency of the braking system.
In order to solve this problem, a central bridge constrained at the half caliper on the support side and free at the half caliper on the external side, also has been used. In this solution, the central bridge receives the tangential forces from the pads and relieves them on the caliper supports so as to prevent relieving the tangential forces on the half caliper on the external side. This solution, however, does not prevent the “twisting” deformations of the caliper body when the central bridge under the load gets deformed, abutting against the external half caliper. Moreover, the deformation of the central bridge causes a certain delay in the braking response which for a racing vehicle is unacceptable. Moreover, since such a bridge is free at a half caliper, it offers no resistance to the axial deformations of the caliper body.